The general requirement to realize a drive that exhibits an extremely low position deviation given load fluctuations and thus behaves rigidly can be of importance in different usage cases. An important example is provided in electrographic printing or copying devices in which a plurality of drive elements must run with high uniformity because fluctuations in the drive lead to a position error in the print product, in particular in color printing. An example results from WO 98/39691 A1, which is included in the disclosure. There a printing or copying device is described with which color printing is possible. Here the individual color separations are collected on a transfer belt in the color collection mode. When all color separations for the print image are collected, the recording medium (for example a paper) is pivoted onto the transfer belt and the print image is transfer printed. It is then simultaneously begun to collect the next color separations on the transfer belt. Since the recording medium and the transfer belt do not exhibit the same surface speed, after the pivoting of the transfer belt between recording medium and transfer belt a force develops that leads to a change of the drive torque of the transfer belt. The force (and thus the torque change) is determined and limited by the contact force of the transfer belt on the recording medium and the friction coefficient between them.
Due to the change of the load torque while the recording medium is pivoted onto the transfer belt, the load angle of the drive motor for the transfer belt also changes, whereby this chases after its desired position (desired position: position at which the transfer belt would be if the recording medium had not been pivoted onto the transfer belt). An offset of the color separations transferred from the intermediate image carrier (for example a photoconductor belt) onto the transfer belt thereby results while the transfer belt is pivoted onto the recording medium to which color separations are transfer-printed from the intermediate image carrier onto the transfer belt is the transfer belt is pivoted away from the recording medium. The offset can amount to approximately 100 μm. The drive torque can thereby change by 1 Nm to 5 Nm.
Upon pivoting of the transfer belt away from the recording medium the force transferred between the recording medium and the transfer belt is abruptly removed. The drive torque for the transfer belt thereby also changes suddenly, whereby on the one hand the transfer belt again runs with the original load angle and on the other hand the transfer belt is shifted into oscillations. Both effects cause a displacement of the color separations. The amplitude of the oscillation can amount to approximately +/−100 μm.
It is an object to specify an arrangement in which the load angle of the drive moment is kept constant in spite of alteration of the driven load.
In a method or system for driving a load element, a drive motor is provided on a drive shaft of the load element that establishes a drive rotation speed of the load element. A rotation torque sensor on the drive shaft emits a load torque signal proportional to a rotation torque. A rotation torque influencing device generates a supplementary torque when the load torque signal deviates from a desired load angle value present when a change has not occurred to a load created by the load element and acting on the drive motor, the supplementary torque being added to a drive torque generated by the drive motor such that a load angle of the drive motor remains substantially constant and uninfluenced by a change of the load.